Radial Magnetic Compression of DIII-D Plasmas

Radial magnetic plasma (R) compression technique will be applied to DIII-D tokamak NBI heated plasmas. The objective is to improve fusion performance. Therefore, it is important to learn how the energy confinement τ_E, density n_e, electron T_e and ion T_i temperatures, plasma current I_p, toroidal field B_T, and toroidal velocity v_Φ evolve during the R-compression and how these interdependent quantities vary with the compression time τ_c and compression factor C_R. Here, C_R ≡ Ro(i)/Ro(f), and i/f refer to the initial/final positions of the major radius R_o. High-performance plasmas (H-mode, τ_E ~ 0.13-0.16s) will be compressed using relatively fast R-compression (τ_fc = 0.02-0.10s) with modest values of C_R = 1.15-1.22, and compare the results with those of a reference campaign that used slow R-compression τ_sc ~ 0.5s [C.M. Greenfield, N. Fus., 37(9), 1215 (1997)] which, nevertheless, led to high performance showing VH-like features (higher v_Φ, similar n_e, T_e, and τ_E, but higher T_i thus higher triple product). R-compression at both slow and fast rates are achieved by ramping up the major equilibrium vertical field. Relative to the reference campaign, with the shorter τ_c and the expected similar τ_E thus τ_c ≡ τ_fc < τ_E, we expect to observe some level of adiabatic R-compression benefits predicted by adiabatic scaling law [H. P. Furth and S. Yoshikawa, Phys. Fluids, 13(10), 2593 (1970)]: increase in n_e, T_e, T_i, I_p, B_T, and v_Φ. Therefore, higher triple product is expected. The Next Step Fusion Simulator will model the R-compression.